1. Field of the Invention
This invention relates to a non-interlace television for multi-color standards, and more particularly to a video signal processing circuit for carrying out sequential scanning, so called non-interlaced scanning suitable for such a television.
2. Description of the Prior Art
As the standard system of the television broadcasting system, there are known the NTSC system, the PAL/SECAM systems, and the like. Video signals of these standard systems carry out interlaced scanning to constitute pictures.
The relationship between time and respective lines in the fields in such an interlaced scanning is shown in a model form in FIG. 5.
In the case of the interlaced scanning, by carrying out the vertical scanning twice, one picture is constituted. Each vertical scanning is called a field scanning. For example, in the case of the television signal of the NTSC system, since the number of lines is 525, the number of lines by each vertical scanning is 262.5.
In FIG. 5, the time t is taken on the abscissa, and horizontal scanning lines (lines) of which vertical positions are determined in accordance with the vertical scanning in a picture of the television are taken on the ordinate V wherein these lines are represented by circular marks 40 of the solid-lines, respectively. Respective fields are indicated every time interval T. Further, since the interlaced scanning is carried out, lines of the next field 42 subsequent by one field to respective horizontal scanning lines (lines) of the field 41 are arranged so as to fill the portions between respective lines of the field 41 earlier than the field 42 by one field. As stated above, in the interlaced scanning, one frame is constituted by two fields, e.g., fields 41 and 42. Accordingly, the number of lines in one field is (525/2) in the case of the NTSC system as stated above, and is (625/2) in the case of the PAL/SECAM systems. Further, when respective television systems are viewed in terms of the field scan interval T, in the case of the NTSC system, field scanning every (1/60) sec., i.e., field scanning of 60 fields/sec. is carried out. On the other hand, in the case of the PAL/SECAM systems, field scanning every (1/50) sec., i.e., field scanning of 50 fields/sec. is carried out.
As stated above, the line scanning system varies in dependency upon a television standard system adopted. Particularly, in the NTSC system having a smaller number of lines, e.g., at the boundary in the vicinity of a vertical scanning, the portion on the upper side thereof is a black region and the portion on the lower side thereof changes to a white region. In the case of such a picture to uniformly change in a lateral direction of the picture, a phenomenon such as a line flicker such that it looks like that its edge portion fluctuates, etc. occurs, resulting in lowered picture quality. In order to improve such an undesired picture quality, various systems such as the sequential scanning system, etc. are proposed.
In the case of television signals of the NTSC system, for example, as represented by the so-called clear vision, in order to improve the picture quality, the motion adaptive non-interlace signal processing technology is used with a view to elimination of the above-described line flicker disturbance, and improvement in the vertical resolution. Accordingly, when such a non-interlace signal processing technology, is employed, a picture free from flicker and having a high vertical resolution can be constructed.
On the other hand, signals of the PAL system and the SECAM system have a low field frequency of 50 Hz. Since, such signals can constitute only 25 pictures in one second, a human being may visually recognize flicker over the entirety of the picture, i.e., so called face flicker. As the method of improving the picture quality against a face flicker, a flicker free technology to drive signals at a field frequency of 100 Hz is used.
Meanwhile, in recent years, there have been many implementations of a large screen of the television also in televisions of the PAL system and the SECAM system. In a large screen like that of an NTSC projector system, line flicker is more conspicuous than face flicker.